1. Field of the Invention
This invention relates to stable aqueous emulsions of water-insoluble particles useful in the cosmetic, pharmaceutical, paint and ink industries.
2. Reported Developments
The prior art has expended great effort to provide stable emulsions of particulates for various applications in the above-mentioned industries. The main problem encountered with emulsions is inadequate physical stability whereby the particulates flocculate, agglomerate and settle-out from the emulsions and become non-uniform.
U.S. Pat. No. 3,133,893 discloses pigment particles coated with a polymer for coloring of plastics, resins and synthetic fibers. The polymer is a thermoplastic, linear, addition polymer of a compound containing the polymerizable group of ##STR1##
U.S. Pat. No. 3,544,500 discloses a process for encapsulating solid particles for use in insecticides, pharmaceuticals and powders. The process comprises adsorbing a polymer on the surface of the particles and providing a stabilizer having an anchor group which become associated with the adsorbed polymer on the surface and a pendant hydrophilic component solvated by the aqueous phase and provides a stabilizing sheath around the solid particles.
U.S. Pat. No. 3,580,880 discloses a process for making dispersions of particulate solids by dispersing the particulate solids in a lipophilic or a hydrophilic liquid in the presence of a polymeric amphipathic stabilizer which associates with the surface of the particles and provides a solvated steric barrier around the particles.
U.S. Pat. No. 4,421,660 discloses a process for preparing compositions comprising the steps of:
emulsifying a hydrophilic emulsion polymerizable monomer in an aqueous dispersion of discrete particles of an inorganic solid; and PA1 polymerizing the monomer to coat the discrete particles of the inorganic solid. PA1 a) preparing a solution of from about 0.01 to about 5% w/w of a wetting agent in an organic solvent to obtain a wetting solution; PA1 b) mixing of 1 to 90% w/w of a finely divided powder having 50 to 100 nm particle size distribution with the wetting solution to obtain a dispersion; PA1 c) mixing the dispersion with of from about 10 to about 99% w/w of an oily/polymeric substance dissolved in an organic solvent to obtain an oily suspension; PA1 d) preparing an aqueous solution by mixing in water of from about 0.1 to about 2.0% w/w of an emulsifying agent selected from the group consisting of a cationic, nonionic, anionic and zwitterionic surface active agent by stirring for about 30 to 90 minutes at a temperature of from about 60.degree. to about 70.degree. C. to obtain an aqueous solution; PA1 e) cooling the aqueous solution to room temperature; PA1 f) adding from about 20 to about 35% w/w of the oily/polymeric suspension to from about 65 to about 80% w/w of the aqueous solution and mixing them for about 20 to 30 minutes at room temperature to obtain an aqueous suspension; PA1 g) emulsifying the aqueous suspension by using emulsifying means, such as a sonifier to obtain an emulsion which contains organic solvents used in step (a); and PA1 h) removing the organic solvent by stirring/evaporation or other means to obtain a final emulsion essentially free of the organic solvent.
While the above-listed and similar approaches made great strides in satisfying the needs of various industries, they do have some shortcomings including the complexity of the processes and less than the desired stability in the products produced thereby. The present invention intends to provide solutions for these and other shortcomings.